Field of the Invention
The present invention relates to the activation of suitably reactive chemistries across an interface after initiating a chemical reaction using a deeply penetrating form of ionizing energy including x-rays, gamma radiation, and e-beam. The present invention covers methods of use, to enable generation of a reactive species, such as radicals, cations, anions, etc, and subsequently bond formation across an interface, particularly polymers bonding, and more particularly to methods for using direct bond scission and reactive species generation of reactive chemistries under X-Ray, e-beam and UV radiation and thermal energy in applications where two objects become bonded across their interface in the absence of direct line of sight.
Discussion of the Background
Adhesives are well known and are used for a wide variety of applications. One particularly important application domain is in the field of manufacturing and assembly, where thermoset adhesives are used to bond one material to another material. Commercially available materials are formulated to meet various requirements, and in addition to the monomer(s) may contain particulate fillers such as metal, oxides, or dielectric powders, as well as various additives to control thermal conductivity, viscosity and other properties. The adhesive materials are typically dispensed as a thixotropic fluid in precise locations, and after all the parts are placed, the entire assembly is heated to a temperature necessary to polymerize the monomers or crosslink resins. The adhesion of two objects is done by adding the adhesive material at the interface of two objects to be bonded. The potential elimination of the addition of a third layer (the adhesive in this case) would be of great benefits. The tool used to dispense an adhesive is eliminated and the step required to cure the adhesive under heat is also rendered obsolete which saves overall cycle time.
As modern assembly methods evolve and more process steps are streamlined for a more efficient and more vertically integrated process, the steps needed to maximize assembly tool utilization, the permissible thermal budget and process cycle time during assembly continue to decrease. Faster manufacturing and higher yields are always of great benefit to the manufacturers.
The clear limitation of conventional photoinitiators is the need to have direct line-of-sight access to a suitable light source. The clear limitation of conventional thermally activated adhesive is the inherent poor thermal conductivity of the materials to be bonded which results in a long process time. The direct welding of two interfaces would be highly desirable. A further disadvantage of thermal activation of adhesives is the potential thermal expansion mis-match when bonding unlike materials to one another.
Furthermore, the assemblies used for various commercial products are relatively small. While electron beam can deliver a desirable source of radiation, the electron beam is not compact and is more applicable to large form factors (such is the case of a wide web process for example). X-Ray energy is delivered through a more compact set of equipment and can be integrated in various tools for more efficient tool utilization.